This invention relates to ultraviolet (UV) radiation monitors, particularly to such monitors which are adapted to field use and, hence, are readily portable and rapid acting.
A recommended UV radiation exposure standard has recently been developed and published by the American Conference for Governmental Industrial Hygenists. The standard is in the form of a curve of maximum energy density v. wavelength and is seen in FIG. 1 which will be described in detail below. The standard represents a rather arbitrary average of a number of conflicting data, covering the short and long term effect of UV exposure on the eyes and various parts of the body.
Time after irradiation is a very important parameter and so is the level of skin reaction considered. The most recent data concern skin reaction at trunk locations and describe the energy requirement of the minimum perceptible erythema. These data correlate satisfactorily with the action spectrum of photokeratitis, supporting a common standard about skin erythema and photokeratitis. The standard was established to be generally below the action thresholds published at various wavelengths. Although it is possible to find data supporting a number of curves differing very significantly from the proposed standards, the latter represents a valuable guide and the maximum energy densities proposed at each wavelength are likely to be safe for all but especially photosensitive individuals.
The principal advantages of the standard are that the standard is a compromise between short and long term effects, different sensitivities of different parts of the body, that it is below the exposure thresholds measured by most investigators, that it is a single spectral curve, eliminating the complexities of multiple standards. As such, the standard is regarded as a guide, or a target with a spectral response within the limitations of real life monitors.
UV monitors for field use have generally been relatively simple instruments using suitable absorbents or filters to insure that mainly radiation within the UV spectrum is effective to excite a suitable photocell. Generally, however, no attempt has been made to shape the characteristic response of the simple UV field monitors to a specific standard. Those UV monitors which have a characteristic response shaped to the aforementioned standard have been heavy and expensive, being complex and difficult to produce, and slow acting. The slow speed of these latter UV monitors together with their relatively inconvenient form have combined to compromise the health and safety of their operators.